Bunks on Alum boats with hull strakes -Where to place bunks?

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overboard
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by overboard » 20 Apr 2018, 11:08

I have two 2x4's setting upright on one of my trailers, but it also has a wider center board that goes down the middle, so there are 3 load bearing surfaces on the hull, that was set up for a 1654 FB GRIZZLY and never had a problem.
On a V hull I would put V type rollers down the center for the keel to rest on, and then either 2x4's on end or do as Ldubs suggested, I also try to keep the bunks between the chines for centering the boat on the trailer and so that it doesn't shift too much side to side while trailering.

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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by LDUBS » 22 Apr 2018, 13:54

Soooo, whatever you decide, fine tune your bunks so the boat sits just right. Add some tall side guides and adjust them so the boat has minimal side-to-side movement. If everything is adjusted just so, when you pull the boat out it will settle right down on those bunks just where it is supposed to sit.

Have fun.
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Tin Man
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by Tin Man » 22 Apr 2018, 17:07

I'm leaning on ripping a 2x4 to a 2.5" width.

Concerns about other option: On ends, and adding a ripped 2x4 on top of a 2x4, reduces the flexibility of such bunk. Although there is not much curvature to my hull, there is some and I would want the bunk to flex as needed.

I'm just wondering if a ripped 2x4 (2.5"X3/12") is enough strength for the weight of hull (300#), outboard (160#), battery, fuel, gear, etc (440#) APPROX TOTAL 900# ?

???
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LDUBS
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by LDUBS » 22 Apr 2018, 22:07

Tin Man wrote:I'm leaning on ripping a 2x4 to a 2.5" width.

Concerns about other option: On ends, and adding a ripped 2x4 on top of a 2x4, reduces the flexibility of such bunk. Although there is not much curvature to my hull, there is some and I would want the bunk to flex as needed.

I'm just wondering if a ripped 2x4 (2.5"X3/12") is enough strength for the weight of hull (300#), outboard (160#), battery, fuel, gear, etc (440#) APPROX TOTAL 900# ?

???

You are saying you want to rip a 2x4 (1.5x3.5) down to 1.5x2.5. Personally, I would not do that. Instead, I would elect to use the 2x4 on edge as previously discussed. This is a very common approach. In fact I may see as many "on edge" bunks for small boats as I do flat bunks. I don't think I have ever seen a 1.5" x 2.5" bunk (and yes, I do think I would notice). In my mind, there must be a pretty good reason why "on edge" 2x4 bunks are so commonly used -- they work.

The downsides have already been mentioned. First, you probably should invest in new bunk brackets for the "on edge" config. These are pretty affordable. Second, your boat will sit 2" higher which could make it harder to launch or recover. As already suggested, perhaps you can adjust your bunk brackets down to offset this.

Another suggestion I would offer is when all is said and done, make sure your boat's transom is fully supported by the bunk right under the transom.

(BTW, 440# for gaso, batteries, and other gear seems like a lot, IMO.)

Edit: I meant to also say you might have to bevel the top edge of the 2x4 bunk to match your hull dead rise angle.
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by WV1951 » 28 Apr 2018, 19:18

Does your trailer not have any center rollers for the middle rib/strake to rest on?

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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by Tin Man » 02 May 2018, 00:23

Update....

Rollers:
I added a 12" roller far forward (hull has scrapped tongue in past) and flipped the oem forward roller back towards stern. This will prevent hull from ever touching/scrapping any metal part of trailer. I have been told by builders (Gregor and Klamath) to NOT allow boat to rest on rollers....weight should be carried by bunks. Based on this info I set rollers down as low as possible and raised bunks a little to achieve virtually no weight on rollers; they just kiss the boat. I can actually turn the rollers by hand which tells me that are adjusted properly.

Now, Bunks Boards update....

With all of the input and advice, it got me thinking.....

Since I want the bunks to flex to curve of hull and also flex while traveling down bumpy roads.....

A. Upright 2x4s would not allow as much flex as laying down 2x4s (standard mounting method)
B. Adding a 2x2 on top of 2x4 reduces flex tremendously
C. How about notching the 2x4 .....down to 2.5" wide (width between strakes) and 1/2" down (depth of strakes). This will allow use of 2x4 flat, allow for flex, and still fit snugly between strakes. Would there be enough wood after this notching to allow for solidly/firmly attaching the 2 lag screws?

Thoughts on C?

Thanks

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richg99
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by richg99 » 02 May 2018, 08:07

Hmmmm. You are placing a lot of emphasis on allowing the bunks to bend to the curve of the hull.

I may be wrong, but I see Support as Support.

Walking near a line of trailers at any launch site, I don't recall seeing any that curve to fit????

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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by LDUBS » 02 May 2018, 12:51

My old boat was a 15' Klamath. The manufacturer was very clear that the boat should be supported on the trailer by the bunks at the transom and the roller up front under the bow stem.

PS: Agree you are probably overthinking the bunk flex thing.
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by WV1951 » 02 May 2018, 16:09

I am having trouble getting a grasp on this whole thing. My Mirro has a very heavy duty rib running the entire length the of middle. With the fact it is a rib, makes it doubly rigid and of course is riveted to the hull. There are two additional ribs/strakes in the same line next to the middle one. I would think this would make for a very rigid hull and supporting the weight would not be a problem. My trailer has two middle rollers, plus the bow stop. The bunks carry most of the weight, so the rollers would not be carrying that much.
When I had my boat upside down when painting, I saw no indication of the middle rib having any bend what so ever. The boat is 40 years old.
Maybe I am missing something.

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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by Tin Man » 02 May 2018, 21:33

LDUBS wrote:My old boat was a 15' Klamath. The manufacturer was very clear that the boat should be supported on the trailer by the bunks at the transom and the roller up front under the bow stem.

PS: Agree you are probably overthinking the bunk flex thing.

Do you think where my rollers have been set up, they are correctly positioned?

I kept the forward-most roller off of the forward bow portion alum piece and placed it under the center hull strake (is this center strake which is wider that the smaller strakes to port and starboard, called a keel strake)?

I've been know to overthink too much!!

As far as the bunk boards......how does my latest idea sound?
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Tin Man
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by Tin Man » 02 May 2018, 21:34

richg99 wrote:Hmmmm. You are placing a lot of emphasis on allowing the bunks to bend to the curve of the hull.

I may be wrong, but I see Support as Support.

Walking near a line of trailers at any launch site, I don't recall seeing any that curve to fit????
I am thinking that once weight is placed on 2x4s, they flex. Mostly return to shape after weight is removed?
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by Tin Man » 02 May 2018, 21:37

WV1951 wrote:I am having trouble getting a grasp on this whole thing. My Mirro has a very heavy duty rib running the entire length the of middle. With the fact it is a rib, makes it doubly rigid and of course is riveted to the hull. There are two additional ribs/strakes in the same line next to the middle one. I would think this would make for a very rigid hull and supporting the weight would not be a problem. My trailer has two middle rollers, plus the bow stop. The bunks carry most of the weight, so the rollers would not be carrying that much.
When I had my boat upside down when painting, I saw no indication of the middle rib having any bend what so ever. The boat is 40 years old.
Maybe I am missing something.
I believe that is what I am trying to achieve by adding the 12" roller and reversing the forward-most roller to sit under keel strake.

It's the bunk boards that is my latest over-thinking dilemma!!! :shock: #-o
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by LDUBS » 02 May 2018, 23:32

Tin Man wrote:
LDUBS wrote:My old boat was a 15' Klamath. The manufacturer was very clear that the boat should be supported on the trailer by the bunks at the transom and the roller up front under the bow stem.

PS: Agree you are probably overthinking the bunk flex thing.

Do you think where my rollers have been set up, they are correctly positioned?

I kept the forward-most roller off of the forward bow portion alum piece and placed it under the center hull strake (is this center strake which is wider that the smaller strakes to port and starboard, called a keel strake)?

I've been know to overthink too much!!

As far as the bunk boards......how does my latest idea sound?
Hi TinMan. I think I experienced a similar issue and understand why you put the 12" roller where you did. However, IMO it should not be touching the boat when the boat is fully loaded on the trailer. The only roller that should be touching the boat when fully loaded is the one under the bow (the one you flipped back). Take a look at page 126 of the "Pic of Your Boat" category. Captain Morgan has a side view pic of his boat on the trailer. While his boat is shorter than yours, in my mind that same concept should work for you. Hope this helps.

As far as the bunk configuration, if it were me I still think having them on edge is easiest and will work well to support your boat.

Also take a look at WV1951's thread just adjacent to this one. He has a great pic of his trailer without the boat. That same set up should work well for you. WV1951 and I might debate the need for the rear-most roller but the concept is still the same. (sorry about all the edits).
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by Tin Man » 03 May 2018, 22:44

LDUBS wrote:
[/quote]Hi TinMan. I think I experienced a similar issue and understand why you put the 12" roller where you did. However, IMO it should not be touching the boat when the boat is fully loaded on the trailer. The only roller that should be touching the boat when fully loaded is the one under the bow (the one you flipped back). [/quote]

What would be the reason for the rear roller not touching hull when loaded but the front roller can touch? Currently, both rollers can be turned by hand while boat is loaded.....this indicates full hull weight is supported by bunks.

To achieve what you suggest, I would have to raise forward roller higher than rear roller, as rear roller is bottomed out on its bracket. Front roller is not as easy to raise in multiple increments.

I also was wondering under which portion of the bow should the forward roller be resting......forward-most bow aluminum (from tip of bow down to where it connects with keel strake) or slightly larger center keel strake?
And why?
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Bunks on Alum boats with hull strakes -Where to place bunks?

Post by LDUBS » 04 May 2018, 19:36

Tin Man wrote:LDUBS wrote:
Hi TinMan. I think I experienced a similar issue and understand why you put the 12" roller where you did. However, IMO it should not be touching the boat when the boat is fully loaded on the trailer. The only roller that should be touching the boat when fully loaded is the one under the bow (the one you flipped back). [/quote]

What would be the reason for the rear roller not touching hull when loaded but the front roller can touch? Currently, both rollers can be turned by hand while boat is loaded.....this indicates full hull weight is supported by bunks.

To achieve what you suggest, I would have to raise forward roller higher than rear roller, as rear roller is bottomed out on its bracket. Front roller is not as easy to raise in multiple increments.

I also was wondering under which portion of the bow should the forward roller be resting......forward-most bow aluminum (from tip of bow down to where it connects with keel strake) or slightly larger center keel strake?
And why?[/quote]

My reasoning for not having the rear-most roller against the boat in your application is to avoid putting a divot in the bottom of your boat. Keep in mind it is not needed to support the boat. You would be adding a third contact point between the front and rear supports. If it is not perfectly adjusted and if the boat & trailer don't move as a single unit, that roller can act as a pivot point when your boat bounces. I don't think I'm describing this very well, but hopefully you get what I mean. Note that others do not share this concern and I am sure you will find plenty of examples of multiple rollers along the keel. Ultimately it is your call.

I hate like heck to open another potential can of worms here, but you say the rollers are close but not touching. I'm not sure how 100% of your boat is supported by just the bunks. If (when) your boat bounces just make sure it won't be pounding against one of both of those two rollers.

I'm not an expert. This is all just my opinion based on my experience with a similar boat and the guidelines given by Klamath.
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